{
Antonov_Kirill
19.09.2012.
this program is to find the max. number of bottels.
}
program Thirdnumber;

{$APPTYPE CONSOLE}

uses
  SysUtils;

var
  i, a, n: integer;

begin
  readln(n);
  a:=0;
  if ((n mod 2)=0) then
  begin
    for i:=1 to (n div 2) do
      a:=a+i*2;
  end
  else
  begin
    for i:=1 to ((n-3) div 2) do
      a:=a+(2*i+1);
    a:=a+n;
  end;
  writeln(a);
  readln
end.
 